This invention relates to a method for automatic remote identification of electronic tags (also known as radio or RF tags) each one of which has its own code consisting of digits, from a station. It also relates to a station for remotely identifying electronic tags each having its own code consisting of digits together with an index representing the position or rank of a digit within said code, notably for implementing the method.
The invention also relates to an electronic tag having means for communicating with a station, for receiving interrogation or polling signals from the station and sending responses to the station along with control means and means for storing a code consisting of digits, notably for implementing the method. The invention also relates to a combination of the station and tags.
The invention generally relates to the field of interrogating electronic tags remotely from an inquiry station or exit gate or the like. Numerous applications are possible, in widely-ranging field. The following can be given as examples:
checking, checking out and/or verifying electronically-tagged articles purchased by supermarkets customers; PA1 counting of tagged objects for stock management in a factory or industrial plant; PA1 recognizing and orienting tagged objects such as, for example, suitcases in an airport; PA1 recognizing the passage of objects fitted with tags, such as for example automobiles at a pay station, and exchange of information with such objects; PA1 in systems for restricting access or for monitoring access of persons carrying an electronic tag to an installation or site, etc. PA1 (a) determining if tags exist having one of possible digits at a certain digit position or rank in their code; PA1 (b) prior to a last digit position, determining if tags exists for a given digit, storing this digit and then temporarily blocking all other tags, and returning to step (a) for the next digit position; PA1 (c) at a last digit position, determining if a tag exists for a given digit, storing this digit and reconstituting a tag code using said stored digits. PA1 determining if tags exist having, at a digit position in their code, a digit that is comprised in a set of digits; PA1 if such tags do exist, then determining whether tags exist having one of the digits of said set at said digit position in their code; and PA1 if such tags do not exist, determining if tags exist having one of the digits of the complementary set of said set at this digit position of their code. PA1 at least two steps consisting in determining whether tags exist that have, at a digit position in their code, a digit that is comprised in a set of digits, the cardinal number of a set in one of said steps being lower than the cardinal number of the set in the preceding step; PA1 a step consisting in determining if tags exist having one of the digits in a set corresponding to the last of said two steps. PA1 a step for determining if tags exist having, at a digit position in their code, a digit comprised in the set {1,2,3,4}; PA1 if a result of this first step is positive, a step consisting in determining if tags exist having at a digit position in their code, one of the digits of the sets {0,1,2}, {3,4}; PA1 if a result of said first step is negative, a step consisting in determining if tags exist having one of the digits of the sets {5,6}, {7,8,9}. PA1 and then proceeding to step (a) for identifying a next tag. PA1 (e) returning to a previous digit position, and unblocking those tags which were temporarily blocked at said previous digit position; PA1 (f) determining if tags exist having one of possible digits at this digit position in their code, and returning to step (b) if such tags exist, and otherwise, proceeding to step (e). PA1 and then proceeding to step (a) for identifying a next tag. PA1 a start-off-analysis instruction D; PA1 an instruction A for advancing an index position in said tags; PA1 at least one interrogation for determining whether a given digit at a digit position in said code corresponding to said index is present in said tags.
Other applications are possible.
In the remainder of this specification, the term "tag" will simply be used to designate an electronic or radio tag, independently of its physical support or use.
The term "gate" or "station" will generally be used for the station from which tags are polled; the physical form of this station is obviously not limited to the physical structure of a frame or gate.
The terms interrogation and polling (a variety of which is sometimes called probing) as used herein refers to a process in which an inquiry station interrogates tags in order to exchange information with them, if necessary.
Systems for remotely polling tags carrying a code already exist.
French patent application 2,648,593 discloses a method and device used for inventory purposes consisting in sequentially polling tags carrying a code, and successively transmitting polling signals corresponding to the first, first two, first three, possible bits of the tag code. Here, only those tags for which the start of the code corresponds to the polling signal reply.
European Patent application EP-A-0,161,779 discloses an identification system in which transponders carrying their own code respond to a station interrogation signal. The data broadcast by each transponder is of a predetermined length and includes an error correcting code; the station can thus detect collision of responses, in other words simultaneous or overlapping responses from different transponders. If the station detects no error, it retransmits the code it receives; the transponder compares this signal with its own code; where they agree, the transponder sends an acknowledgement signal and goes into standby mode; otherwise, it goes on standby over a random number of cycles before starting to broadcast again.
European Patent application EP-A-0,242,906 discloses a system for identifying tags which can apparently only operate with one single tag, and in which it is suggested that the tag be reprogrammed during predetermined intervals of the signal broadcast by the station, after the tag is recognized.
European Patent application 0,494,114 discloses an electronic identification system in which the tags respond after a random time interval of the type of that described in European Patent application 0,161,779.
European Patent application 0,495,708 discloses a system for communication between a base station and mobile terminals, in which the mobile terminals respond to a polling signal within a time window which depends on the first digit of their code; the tag response signal is of the type in EP-A-0,161,779, providing collision management.
Additionally, U.S. Pat. No. 4,071,908 discloses a system for polling terminals over a line, in a completely different context from that of the invention, and further implementing a principle similar to that in FR-A-2,648,593. The polling context in this patent involves frequencies that are much higher than those usually employed for tags, and the problem of optimizing transmission duration does not arise. In this document, interrogation consists in sending a complete code. Moreover, the method proposed in this document has no sense unless the number of terminal stations in the system is known.
European patent application 0,669,591 discloses a remote information transmission system. Here, successive determinations are made to investigate if a transponder is in one half of the total number of tags, and, if this is the case, dividing the set of transponders into two, and continuing to do so until only one single transponder is left. Transponders reply to each interrogation by issuing their code, followed by an error correction code. This document only discloses the method known as a dichotomizing (binary) search, and does not propose determining if tags or transponders exist having one of a set of possible digits at a certain digit position in their code. Nor is there any suggestion of blocking the tags or transponders, and, consequently, this would not be useful, due to the presence of error correcting codes.
French patent application 2,677,135 discloses a method for remote interrogation of tags carrying a binary code. Here, it is proposed to interrogate the tags at each step using questions that depend on the proceeding step. The method in this patent does not operate for codes that are not binary, and cannot simply be envisaged for non-binary codes. In binary, this method involves full scanning of the complete code, starting from the first digit and proceeding to the last, which can be detrimental to the time needed for interrogation.
These systems suffer from disadvantages.
They are hardly suitable for solving the technical problem involved in simultaneously, and rapidly interrogating or polling a large number of tags. Indeed, they often require long messages both at station and tag level, which, notably in the case of low frequencies, lengthens the total polling time.
Collision avoidance or management between responses multiplies exchange of information, and lengthens polling time; the use of random periods of time increases total polling time where a large number of tags are involved. There is additionally the problem of generating random numbers, notably in the case of a large number of identical tags.
Finally, the above solutions do not allow fast interrogation of tags, with the ability to adapt to all possible tag code configurations.